Support Dark Mode on macOS

[cliftonlabrum]

Please add a dark theme to Realm Studio for those of us that use dark mode on macOS. 🙂

[bmunkholm]

This is one of those features that we encourage the community to take on.

[mrkulik]

please hurry up, need it so much!

[takameyer]

@mrkulik We don't have capacity right now for this, but there was a pr that someone made. If someone has some time to take that over, we could get that merged :)

[bezenson]

As a person with eye floaters will very appreciate having dark mode in app :)